LM4782, LM4782TABD

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SNAS231B – FEBRUARY 2004 – REVISED MARCH 2013

CLICKS AND POPS

In the typical application of the LM4782 as a split-supply audio power amplifier, the IC exhibits excellent “click”

and “pop” performance when utilizing the mute and standby modes. In addition, the device employs Under-

Voltage Protection, which eliminates unwanted power-up and power-down transients. The basis for these

functions are a stable and constant half-supply potential. In a split-supply application, ground is the stable half-

supply potential. But in a single-supply application, the half-supply needs to charge up at the same rate as the

charging of the amplifier inputs will result in output clicks and pops due to the differential input topology of the

LM4782.

To achieve a transient free power-up and power-down, the voltage seen at the input terminals should be ideally

the same. Such a signal will be common-mode in nature, and will be rejected by the LM4782. In Figure 5, the

the two nodes. This should significantly reduce any type of turn-on pop, due to an uneven charging of the

amplifier inputs. This charging is based on a specific application loading and thus, the system designer may need

to adjust these values for optimal performance.

the 2N3904. But due to the input and output coupling capacitors in the circuit, along with the negative feedback,

rate resulting in a popless turn-on. Adjusting these resistors values slightly may reduce pops resulting from

power supplies that ramp extremely quick or exhibit overshoot during system turn-on.

PROPER SELECTION OF EXTERNAL COMPONENTS

Proper selection of external components is required to meet the design targets of an application. The choice of

external component values that will affect gain and low frequency response are discussed below.

gain is found by Equation 5 below:

(5)

For best noise performance, lower values of resistors are used. A value of 1k

higher than 50V/V. Gain settings below 10V/V may experience instability and using the LM4782 for gains higher

than 50V/V will see an increase in noise and THD.

by these two components. The -3dB point can be found from Equation 6 shown below:

(6)

If an input coupling capacitor is used to block DC from the inputs as shown in Figure 6, there will be another high

set the DC bias point on the amplifier's input terminal. The resulting -3dB frequency response due to the

(7)

HIGH PERFORMANCE CONSIDERATIONS

Figure 5, and Figure 6) will result in very good performance. However, electrolytic capacitors are less linear than

other premium capacitors. Higher THD+N performance may be obtained by using high quality polypropylene

capacitors in the signal path. A more cost effective solution may be the use of smaller value premium capacitors

in parallel with the larger electrolytic capacitors. This will maintain signal quality in the upper audio band where

any degradation is most noticeable while also coupling in the signals in the lower audio band for good bass

response.

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